1. Field of the Invention
This invention relates to printing machines for labeling plastic containers, and, more particularly, to head construction for supporting the dies or markers. It can be used to decorate or mark plastic surfaces other than containers.
2. Description of the Prior Art
Prior printing machines usually include a reciprocable ram having a head located at its lower end for supporting a marker or die. An anvil is mounted in a suitable block beneath the head for retaining a workpiece in an operable position. A film having a layer of coating material, such as an alkali metal or marking pigment, is inserted between the marker and the workpiece. The marker or die is heated and functions to release the coating material depositing it on the surface of the workpiece. Although such devices are used extensively, they suffer various shortcomings severely limiting their utilization for container labeling. A major constraint of these machines is that they are relatively large and bulky, and usually operable on limited types of workpieces such as flat objects or plastic wire. Many plastic bottles and containers are unsuitable on such machines for assembly line production. The reason for the problem lies in the head construction of the apparatus. In prior devices the heads are rigidly mounted on the machine and are unable to function resiliently and automatically with the work piece, so as to conform to the configuration of the printing surface. As a result, upon contacting the workpiece, the dies do not adjust to the contour of the work piece nor compensate for any misalignment. Many bottles won't fit or go through the machine. Furthermore, prior devices did not have the capability of individually controlling the temperature of each of the dies which is undesirable because of the different heating characteristics of the various dies and color plates.